1. Field of the Invention
Recently, a throttle valve controller for an engine, especially a vehicular throttle valve controller has been required to satisfy various requirements, and some of such requirements are as follows:
(1) If any slippage of a wheel occurs, the throttle valve must be actuated toward its closed position, regardless of depression of an accelerator pedal, so as to eliminate the slippage:
(2) Opening and closing of the throttle valve must be controlled based on the modified manipulated amount of the accelerator pedal in response to the driving condition of the engine;
(3) The throttle valve must be controlled so as to obtain a constant vehicle speed, regardless of the manipulated amount of the accelerator pedal by a driver; and
(4) During shifting of an automatic transmission, the throttle valve must be actuated toward its closed position.
In order to satisfy these various requirements, there has been proposed an apparatus wherein the throttle valve is controlled by an electromagnetic actuator. Such an electromagnetic actuator is effective to meet the above requirements (1) to (4). However, such an electromagnetic actuator and a control unit therefor may suffer from a breakdown. To assure safety, there has been developed a throttle valve controller which is provided, in addition to the electromagnetic actuator, with a mechanical control transmission path for mechanically transmitting depressed force of the accelerator pedal to a throttle shaft. The present invention relates to a throttle valve controller of this type.
2. Description of the Prior Art
In order to meet the above requirements (1) to (4) in such a throttle valve controller, the electromagnetic actuator and the mechanical control transmission path must be switched to control opening and closing of the throttle valve. For this purpose, there has been proposed a prior art system as shown in FIG. 26, which is disclosed in Japanese Laid-Open Utility Model Publication No. 1-173355.
The prior art system in FIG. 26 includes a throttle valve 60 for adjusting the amount of intake air to an engine, bias means 61 for normally biasing the throttle valve 60 toward its closed position, an electromagnetic actuator 64 for controlling opening and closing of the throttle valve 60 in accordance with a control signal generated from a control circuit 63 in response to the depressed amount of an accelerator pedal 62, an electronic control transmission path 67 for transmitting driving force of the actuator 64 to a throttle shaft 65 of the throttle valve 60, a mechanical control transmission path 68 for mechanically transmitting manipulated force of the accelerator pedal 62 to the throttle shaft 65, a first switching means 51 for connecting or disconnecting the electronic control transmission path 67, and a second switching means 52 for connecting or disconnecting the mechanical control transmission path 68.
In the normal operating condition, only the first switching means 51 is activated to connect the electronic control transmission path 67, allowing normal driving, while, in the abnormal operating condition, only the second switching means 52 is activated to connect the mechanical control transmission path 68, allowing a vehicle to run off the road. The switching means 51, 52 are switched for activation in response to absence or presence of a malfunction signal from the control circuit 63.
In the above prior apparatus, the transmission paths 67 and 68 employ their individual switching means to switch disconnection and connection thereof, so that the two switching means 51, 52 are required, which increases complication in structure and cost.
Provision of the two switching means 51, 52 further involves a possibility of simultaneous connection of both transmission paths 67, 68 when both switching means 51, 52 are activated in error, and in such a case, the throttle valve 60 will become uncontrollable, which causes a defect in reliability.
FIG. 27 shows another prior art system as shown in Japanese Laid-Open Patent Publication No. 1-227825. In this system, a throttle valve 72 has a throttle shaft 73 to which an arm 74 is attached and has an end rotatably supporting a sheave 77 through a pin 75. A return spring (not shown) is attached to the other end of the arm 74 so as to bias the throttle valve 72 toward its closed position. The sheave 77 has a groove in which a cable 78 is trained, the cable having one end coupled with a pulley 80 through a pin and the other end coupled with an accelerator pedal 81. The pulley 80 has a rotary shaft 85 which is connected through an electromagnetic clutch 86 to an output shaft of a motor 87. The motor 87 is controlled by an electronic control unit 97 in accordance with the driving condition of a vehicle.
In the regular or normal operating condition, opening and closing of the throttle valve 72 is directly manipulated by the accelerator pedal 81 through the cable 78, and during traction control or shifting by an automatic transmission, the motor 87 drives the pulley 80 to close the throttle valve 72 irrespective of depression of the accelerator pedal 81. In the faulty or abnormal operating condition, the electromagnetic clutch 86 is turned off to disconnect the motor 87, permitting control of the throttle valve 72 only by the accelerator pedal 81.
In this system, the mechanical control transmission path is kept in connection both in the normal and abnormal operating conditions, and the electromagnetic actuator is used only to close the throttle valve 72 for traction control or the like. Thus, this system can meet the above requirements (1) and (4) but not the other requirements (2) and (3).
In the prior art apparatus in FIG. 27, the electromagnetic clutch 86 is not provided on the throttle shaft 73 of the throttle valve 72 but on the rotary shaft 85 disposed apart from the throttle shaft 73, so that there must be provided between the throttle shaft 73 and the rotary shaft 85 the power transmission mechanism composed of the sheave 77, the pulley 80, the cable 78 and others. This increases complication in structure and the number of parts, causing enlargement in size of the apparatus and reduction of reliability thereof.
Furthermore, the apparatus is so constructed as to cause interference between two valve driving systems of an accelerator system (mechanical control transmission path) and a motor system (electronic control transmission path), which will deteriorate electronic controllability in the normal operating condition as well as accelerating manipulability due to change in the depressed force of the accelerator pedal caused by reaction force thereof.